Electromagnetic radiation detectors and spectrometers are being used to measure the emission of radiation from samples of solids, liquids and gases. Typically, a sample is excited with suitable first radiation to stimulate the emission of second radiation, and the latter is analyzed to identify characteristics of the sample. This general principle is applied in medical imaging, DNA sequencing and other materials analysis, laser scanning, etc.
In a variety of applications it is important to measure the spectral content of electromagnetic radiation, for which purpose spectrometers and calorimeters are typically being used. Other applications involve spectral pattern recognition, wherein specialized signal processing is performed in addition to spectral measurements. In many applications, such as detection and identification of fluorescent objects, it is important to be able to measure selected bands of a received spectrum, and it is often advantageous to be able to change the selection of the measured bands in the course of the measurement.
To measure selected spectral bands, certain known devices scan a dispersed spectrum, or apply signal processing of a spectral image obtained by optical dispersion. Both of these techniques suffer from being relatively slow, so that they are inconvenient where rapidly varying spectral information needs to be processed, such as, e.g., information obtained in spectroscopy of modulated radiation.